This invention relates to a surface wave touch screen for a cathode ray tube (CRT) display panel or other touch-controlled device which is capable of recognizing touch positions along a predetermined coordinate axis on a touch surface. More particularly, it relates to a surface wave touch screen for use in an external environment.
Systems employing a touch screen as a data input device are widely known. By touching the touch screen at a predetermined position with a finger or other object, data is selected that is indicative of that particular position. Thereupon, the associated data is introduced into the system and processed. A touch screen may be combined with a display for selecting data according to the zones shown on the display, such as virtual buttons. Also, the display may function as a means for providing visual feedback to the user by showing the information pertaining to the data after processing.
On the basis of the mechanism for activating the touch screen, several types of touch screens can be distinguished. Touch screens of choice for self service terminals, such as automated teller machines (ATMs), are so-called surface wave touch screens that locate the absorption of surface acoustic waves propagating in a front panel, the absorption occurring as a result of the contact between the panel and a soft tissue such as the user""s finger. These touch screens, which have been on the market since 1980, work exceptionally well, are very stable, have no drift and are very resistant to damage. They are currently the preferred touch screens for heavy use self service terminals in unprotected environments, such as through the wall applications, because they will survive a large amount of abuse and vandalism. They do however have the disadvantage that they are adversely affected by water on the screen. Water is a good absorber of acoustic waves, and hence strongly absorbs the surface waves. Water on the touch screen surface results in a local dead area. Even if the touch screen is inclined or mounted vertically, if exposed to water, droplets can adhere to the screen, rendering it inoperative. Drying the water restores the operation of the screen. For this reason, surface wave touch screens are only suitable for dry or sheltered environments, such as shopping malls, where water on the screen is not a major problem.
It is an object to provide a surface wave touch screen which operates even if water is applied to the surface, and which is thus suitable for use in external environments.
According to the invention there is provided a surface wave touch screen comprising a touch panel capable of propagating surface acoustic waves wherein a touch on the touch panel causes a perturbation of a surface wave propagating through the region of the touch, transmitter and receiver means coupled to the touch panel for transmitting and receiving surface acoustic waves on the touch panel and control means for determining the position of a touch on the touch panel, characterized in that the touch surface is hydrophobic.
By use of a touch surface which is hydrophobic, any water droplets landing on the surface would immediately be shed off the inclined or vertical face of the screen and allow the touch screen to function normally.
Preferably, the panel of the touch screen comprises glass coated with Ritec xe2x80x9cCLEAR-SHIELDxe2x80x9d.
By the use of xe2x80x9cCLEAR-SHIELDxe2x80x9d, the glass touch screen is rendered hydrophobic and anti-static, and its coefficient of friction is reduced. Hence, the touch screen glass becomes a non-stick, easy clean surface, and water and other contaminants are shed more rapidly.